Table 3.3.
Details and period of relative sea-level trends (mm yr-1) for tide gauge stations along the eastern Adriatic coastline with records longer than 35 years (after Marcos and Tsimplis, 2008). Location of tide-gauge stations are shown in figure 3.2.
Name PMSL ref Lat Long Period Length (years) Relative Trend mm yr-1
(1) Trieste 270061 45.65 13.76 1905 - 2006 106 1.2 ± 0.1 (2) Rovinj 280006 45.08 13.63 1955 - 2004 53.58 0.6 ± 0.2 (3) Bakar 280011 45.30 14.53 1930 - 2004 79.00 1.1 ± 0.1 (4) Split I 280021 43.51 16.39 1952 - 2004 56.67 0.7 ± 0.2 (5) Split II 280031 43.51 16.44 1954 - 2004 54.83 0.5 ± 0.2 (6) Dubrovnik 280081 42.66 18.06 1956 - 2004 53.00 0.9 ± 0.2
3.3.2. Site Selection - The Croatian Coast
The eastern Adriatic coastline is the second most indented coastline in Europe, of which Croatia hosts the longest part (Pikelj and Juračić, 2013). With a total length of approximately 5800 km, the Croatian coastline is predominantly rocky and steep with numerous pockets of sand and gravel beaches and few alluvial zones (Baric et al., 2008). The coastal zone is generally very narrow (between 1 – 5 km) where high Dinaric mountain ranges often protrude straight out of the sea (Pikelj and Juračić, 2013). Population density is significantly higher in the coastal zone compared to the hinterland, housing 25.6 % of the total population (Baric et al., 2008). Ten relatively large rivers flow out into the Adriatic Sea along the Croatian coastline, the largest of which is the Neretva River in the Dubrovnik-Neretva
Page | 29 County, with an average discharge of 332 m3s-1 which peaks in December (Orlić et al., 2006).
As a result of the highly indented karstic nature of the coastline, vegetated coastal sedimentary environments are a rare habitat in this region, with only one large alluvial plain along the coastline at Neretva in the south. A limited amount of research exists on salt- marsh environments in the Adriatic, with most studies focusing on the Italian and northern side due karstic nature of the eastern coastline. However, a review of salt-marsh vegetation by Pandža et al. (2007) identified eight ecologically important sites in central and south- eastern Adriatic, and two of the sites, Jadrtovac and Blace (figure 3.4), are the focus of this research. Their selection is also based on the close proximity of Jadrtovac and Blace to tide gauge stations at Split, Ploće and Dubrovnik respectively (figure 3.4) where tidal ranges are of comparable amplitude as shown in table 3.1.
Figure 3.4. Study area map showing relative locations of sample sites (a) Jadrtovac and (b) Blace along the Croatian coastline, eastern Adriatic Sea.
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3.3.3. Jadrtovac
The salt-marsh is located on the outskirts Jadrtovac (population 200) situated within Morinje Bay (43°40’48”N, 15°57’24”E), approximately 3 km south of Šibenik and 50 km north of Split, central Croatia (figure 3.4). Communication with the open Adriatic Sea occurs through a narrow (150-350 m), 2.5 km-long channel at a depth of 23 m, while at the entrance to the Bay the depth is reduced to 2 m (Šparica et al., 2005a). With a surface area of 3.5 km2 and a maximum water depth of 21 m, the bay can be divided into two sections, with a shallow northern region and a deeper southern channel (Mihelčič et al., 2006). A relatively high sedimentation rate of 1.0 m/ka has resulted in the accumulation of 4.5 m of organic-rich sediment which began approximately 4.5 ka BP as the Morinje depression was inundated during the latter stages of the Holocene transgression (Bačani et al., 2004; Šparica et al., 2005a). The Morinje ecosystem is characterised by varying seawater temperatures (0-35°C) and fluctuating salinities (up to 42‰) as a result of seasonally enhanced evaporation, continuous freshwater supply from onshore and submarine springs and surface runoff events (Bačani et al., 2004; Šparica et al., 2005a). At present, there are no permanent inflows to the bay, and current activities in the surrounding environment are primarily associated with seasonal tourism and agriculture (Mihelčič et al., 2006).
The Jadrtovac salt-marsh is located on the eastern side of the bay (figure 3.5) and is roughly 130 m at its widest point before thinning out moving north around the bay. The mean daily tidal range at this site is approximately 23 cm, derived from values obtained at the nearby Split tide-gauge (Hydrographic Institute, 1955–2002). A table of tidal levels for this site is provided in table 3.4. The salt-marsh environment displays distinct zones of vegetation with
Juncus spp., Halimione, Atriplex, Scirpus spp., Phragmites and occasional Suaeda spp. colonising higher elevations in the upper salt-marsh zone, whilst mid-to-low salt-marsh zones are dominated byHalimione spp., Salicornia spp. and again occasional Suaeda spp. The salt-marsh is intersected by a narrow (~2 m) man-made channel presumably for local fishing access within the bay. Two sample sites were established at Jadrtovac (JD1 and JD2), as shown in figure 3.5, where surface transects were established perpendicular to the coast incorporating all sub-environments from the high salt-marsh zone to the salt- marsh/sea interface. The low salt-marsh/sea interface at JD1 is characterised by a small cliff edge (~10-20 cm). Details regarding the sampling at JD1 and JD2 are provided in table 3.6.
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Figure 3.5. Study site map showing (a) location of salt-marsh environment within Morinje Bay with surface transects, random sampling area and core sites, (b) photo of JD1 sample
site, and (c) photo of JD2 sample.
Table 3.4.
Tidal levels (relative to m HVRS71) derived from Split tide-gauge (Hydrographic Institute, 1955–2002). Lowest astronomical tide Mean low water springs Mean low water neap Mean tidal- level Mean high water neap Mean high water springs Highest astronomical tide - 0.203 -0.036 +0.034 + 0.128 +0.233 +0.256 + 0.284
3.3.4. Blace
Blace is situated approximately 120 km south of Jadrtovac (43°00’15”N, 17°28’27”E) and comprises a remote small pocket salt-marsh just north of a small fishing village (population 200) approximately 10 km south of Ploče (figure 3.4). The salt-marsh is located south of the Neretva River Delta, the largest outflow along the Croatian coastline with a large, 12 000 hectare alluvial plain, representing an important ecological and agricultural site (Romić et al., 2008) and recognised by the Ramsar Convention since 1993. The river originates in Bosnia & Herzegovina and is approximately 255 km long within a catchment area covering over 13000 km2 (Jurina et al., 2013). The lower course of the river however, which flows through the Republic of Croatia, is only 36 km long, flowing through Quaternary alluvial deposits (Orlić et al., 2006).Rising sea level is a particular risk to this region and, combined with
Page | 32 surge-induced flooding, the intrusion of saline waters could have devastating effects on the agricultural practices that dominate this landscape (Baric et al., 2008).
The salt-marsh is located approximately 3 km south of the river’s mouth in a sheltered embayment from the open Adriatic Sea and is roughly 40 m wide. The mean daily tidal range at this site is again 23 cm, as taken from values from the Ploće tide-gauge (Hydrographic Institute, 1955–2002). Indeed, analysis of admiralty tide-tables (Admiralty, 2010) for Ploće revealed an almost identical tidal regime to Split (table 3.4). Distinct zones of vegetation are again apparent at Blace, with Juncus spp., Halimione, Atriplex and Chenopodiaceae spp. dominating high-to-mid salt-marsh zones and Limonium spp. and Salicornia spp. dominating mid-to-low salt-marsh. Two sample sites were established at Blace (BL1 and BL2), as shown in figure 3.6, where surface transects were again established perpendicular to the coast incorporating all sub-environments from the high salt-marsh zone to the salt-marsh/sea interface. Specific details regarding the sampling at BL1 and BL2 are provided in table 3.6.
Figure 3.6. Study site map showing (a) location of salt-marsh environment at Blace with surface transect and core sites, (b) photo of BL1 and (c) BL2 sample sites.
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